Electrolytic hydrodimerization process and extraction procedure



ELECTROLYTIC HYDRODIMERIZATION PROCESS AND EXTRACTION PROCEDURE Filed April 20, 1962 6, 1955 M M. BAIZER 3,193,477

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waited rates Patent U 3,193,477 ELECTROLYTIC HYDRODIMERIZATION PROC- ESS AND EXTRACTION PROCEDURE Manuel M. Baizer, St. Louis, Mo., assigno'r to Monsanto Company, a corporation of Delaware Filed Apr. 20, 1962. Ser. No. 189,072

- 16 Claims. (Cl. 204-43) trolytic'reductivccouplings of olefinic compounds and to apparatus for effecting such procedures.

A general object of the present invention is to provide a procedure for extracting from an electrolyte the reduced, coupled product obtained in the electrolytic, reductive coupling of olefinic compounds in an electrolyte.

A further general object of the present invention is to provide a procedure, to effect the electrolytic reductive coupling of olefinic compounds in an electrolyte simultaneously with the extraction of the coupled product from the electrolyte. A more specific object is to provide a procedure for the hydrodimcrization of olcfinic compounds in aqueous electrolyte and to utilize unrcacted olefinic compound to extract the hydrtxlimcrization product from the electrolyte. A still more specific object of the invention is to provide a procedure for the hydrodimerization ofacryloniti'ile to adiponitrile in which the hydrodimerization occurs in aqueous electrolyte but acrylonitrile is employed in excess of its solubility in the aqueous electrolyte and is used to extract the adiponitrile product from the aqueous electrolyte.

The'apparatus of the present invention is an electrolysis cell for continuous reductive coupling and extraction of the coupled product, the cell being composed of a container, cathode and anode, an electrolyte. an olefinic compound which is dissolved to some extent in the. electrolyte but which is present in excess of its solubility so as to form a supernatant layer over the electrolyte, and an outlet from the cell container located above the surface of the electrolyte. but at a level which permits overflow of the supernatant layer of olcfinic compound. As the hydrodimerization proceeds,-the reductively coupled product preferentially dissolves in the supernatant olefinic compound layer and additional olefinic compound can then be dissolved in the electrolyte to maintain the desired concentration there. Moreover. the additional olefinic compound added to the cell as the hydrodimerization proceeds, is preferentially added below the surface of the electrolyte to promote the desired extraction of the product. In more particular aspects, the overflow of the supernatant layer can flow through a tube or other conduit to a receptacle serving as a boiler, and the unreacted olefinic compound can be distilled from the boiler and returned to the electrolysis cell. The conduit from the boiler can, if desired, be provided with cooling coils, a condenser, or other means to cause condensation of the distillate prior to its return to the electrolysis cell in order to avoid overheating the electrolysis cell. In another embodiment, the apparatus can be provided with a washing chamber in the conduit from the overflow to the boiler. Such a. chamber is provided with an aqueous washing liquid, and an inlet means to permit the overflow from the cell to discharge below the surface of the washing liquid, and the chamber is further provided with an outlet above the surfnce of the washing liquid to permit flow of the organic materials from the washing chamber to the boiler. a

In one particular embodiment, the electrolysis" cell has a catholyte composed of aqueous electrolyte and acrylonitrite and a supernatant layer of acrylonitrile which 18 present in excess of its solubility in'the aqueous electrolyte.

Electrolytic hydrodimerizations and other reductive eouplings of olefinic compounds have previously been described in the copending applications of the present applicant which are referred to hereinbelow. The present invention involves an improvement in electrolytic hydrodimerization or other reductive couplings in that electrolytes are employed which dissolve a sufficient amount of the olefinic compounds to result in efficient coupling, but which are not completely miscible with the olefinic compounds; and the olefinic compounds are employedin such amounts that they form a supernatant layer of olefinic compound above the surface of the electrolyte thereby making it possible for the reductively coupled product to be extracted into the supernatant layer. This makes it possible to continuously maintain a concentration of the olefinic compound in the electrolyte which is suitable for efficient reaction by simply adding the olcfinic compound as it is used up. while the product is continuously'removed by permitting the supernatant layer of olefinic compound containing the reductively coupled product to overflow from. the electrolysis cell. The improved procedure can be etlccted with any olefinic compounds capable of being reductively coupled by electrolysis. It is only necessary to employ the olcfinic compound in amounts greater than its solubility in the electrolyte, and to employ an electrolytc of greater Specific gravity than the olefinic compound, and one which will dissolve a sufiicient amount of the olefinic compounds to permit an efficient reductive coupling. Alternatively, an electrolyte of lesser specific gravity could be employed and provision made for Withdrawing olefinic compound at a regulated rate from the heavier olctinic layer.

In another aspect the invention concerns a procedure for conducting the electrolytic reductive coupling of olefinic compounds in an electrolysis cell, removing the electrolyteand reaction components from the electrolysis cell, by pumping, gravity flow or other suitable means, and employing olefinic compound to extract the reduced coupled product from the electrolyte which can then, if desired, be returned to the electrolysis cell. In'this aspect, excess olefinic compound can be present during the electrolysis. or the olcfinic compound can be present in amounts which are completely miscible with the elec trolyte. It is desirable, of course. that the olefinic compound employed as extractant be one which is being reductively coupled in the electrolysis. The extraction can be conducted by ordinary mixing and decantation, counter current extraction procedures, or other means known to the art, and the olcfinic compound can be separated from the product by distillation or other procedures suitable'for effecting separation of the particular materials. If desired, procedures and apparatus of the type illustrated herein for simultaneously forming, extracting and isolating the reductively coupled product can also be employed for effecting the extraction and isolation separately from the electrolysis. It will bev recognized that such separate procedures include extracting the product from the electrolyte in the electrolysis cell but subsequenrto the electrolysis, as well as the procedure in which the electrolyte is removed to a separate vessel prior to such extraction.

The figure of the drawing illustrates an electrolysis cell suitable for conducting electrolytic reductive coupling reactions andextracting the reduced coupled product from the electrolyte. the cell being adapted to continuous operation, The cell contains electrolyte in a container current and other requirements for an electrolysis cell.

To describe the cell in detail, it is composed of a boiler 1 which is a receptacle in which the overflow from the cell is collected and from which the low boiling components can be distilled,-a riser tube 2 leading to a condenser 3 which is connected to a disperser 4 beneath the surface of the electrolyte in the cell which has a cathode 5, which in this case is mercury resting on the bottom of the container, an electrolyte 6, an anode chamber 7 which is separated from the catholyte by a diaphragm 8,

a lead to the cathode 9, a lead to the anode 10, a

thermometer 11 an inlet tube 12 to 'add materials, for

- example acid, below the surface or the electrolyte, and

a stirre 13. An additional means suitable for adding additional olefinic compound below the surface of the electrolyte is provided by the condenser 3 connected to the disperser 4 The catholyte level 14' is not sufficiently high to permit flow from the container through the overflow, but the level 15 of the supernatant layer of olefinic compounds resting on the catholyte is high enough to permit overflow from thefiask as the electrolysis proceeds, the overflow going into a washer 16 which is a container provided with an inlet tube having a disperser 17,'a 1evel of water 18, a level of the supernatant layer in the washer 19, a stopcock 20' for discharge of the aqueous layer and the overflow tube 21 leading from the electrolysis cellto the inlet tube and disperser of the washer. The washer also has an overflow tube 22 leading to the boiler 1 and the washer has an inlet 23 for addition of more water. It will be recognized that the drawing is merely illustrative and that there can be many variations in the apparatus of the present invention. For example, it is possible to use a solid metallic pole or wire for the cathode, rather than a layer of mercury; it is also feasible to have the same electrolyte as catholyte and anolyte and not to'scparate the cathode and anode by a diaphragm. The stirrer and thermometer are, of course, highly desira-ble but by'no means essential. In the embodiment shown, there is a washer 16, but if desired this could be completely eliminated and the overflow tube 21 could lead directly to'the boiler 1. It will also be recognized that it is not essential to directly connect the boilerl 'by a tube 2 with the condenser 3 which is connected to the inlet to the cell, but that the material collected in 1 could be distilled or otherwise treated to separate the product in any convenient distillation apparatu's, and additional olefinic compound could be added from'any source through the inlet 4 to continue the electrolysis on a continuous basis. It will also be recognized that the boiler 1 could be provided with a stopcock on its lower portion to permit discharge of the distillation residue, or could be adapted for separation from the riser tube to permit removal for treatment of the residue for isolation or other purposes, while being replaced with another boiler to permit the continuance of the electrolysis.

Thepresent invention is adaptable to the reductive coupling of any olefinic compound capable of electrolytic reductive coupling. Among the suitable compounds are the alpha,b eta-olefiniccarboxylates, nitriles and amides as disclosed in my copending applications Ser. No. 163,028, filed December 29, 1961; Ser. No. 145,480, filed October 16, 1961; Ser. No. 145,482, filed October 16, 1961; and Ser. No. 75,130, filed December 12, 1960; all

. 4 i Y of the foregoing applications being incorporated herein by reference. .For example, according to the presently provided process, reduced, coupled products of olefinic compounds can be produced as follows:

1 R. lit. R

where X and Y are selected from the group consisting of cyano,.carboxylate,.and carboxamide groups, and each R. R and R" is selectcdvfrom the group consisting of hydrogen, alkyl (including cycloalkyl) and aryl radicals, particularly such radicals containing no more than eight carbon atoms. It will be recognized that a wide variance in the substituents is permissible, and each individual R, R and R" can be the same as or different from another R, R, or R", X and Y can be the same or different, and also the two finally defined compounds to be coupled can be the same or different. While the illustrative formula shows only one functional group, i .e., X or Y, in each reactive compound, it will be recognized that each olefinic reactant can have two or more such functional groups, and they can be the same or ditferent types. X and Y can be further defined as representing Mcthacrylonitrile Butyl methacrylate' Crotononitrile Ethyl erotonate 2-methylcnebutyronitrile 2-pentenenitrile N,N-diethylcrotonamide N,N-dibutyI-Z-pentenamide N,N-dimethyl-Z-tnethylenevaleramide 2,S-dimethyladiponitrile Dibutyl 2,5-dimethyladipate 3,4-dimethyladiponitrile .Diethyl 3,4-aimeth 1adip 2,5-diethyladiponitrile 3,4sdiethyladiponitrile N .N,N,N-tetraethyl 3,4-dimethyladipamide l-l .N,N',N'-tetrabutyl 3,4-diethyladipamide N,N,N,N-tctramethyl 2,5-dipropyladipamide A few examples of mixed reductive couplings to which the present invention is applicable are:

Methacrylonitrile and ethyl acrylate Crotonitrile and ethyl acrylate Ethyl acrylate and methyl acrylate Butyl acrylate-and butyl methacrylate Ethyl delta-cyano caproat e Ethyl delta-cyano gamma-methyl valerate Ethyl methyl-adipate I Dibutyl 2-methyl-adipate The broad applicability of electrolytic reductive coupling can be illustrated by comparison with the generalized Michael condensation (Organic Reactions, 10 179). In the Michael condensation a donor molecule, YCH Y, in which at least one of X and Y is an activating group, must be capable of furnishing an anion, usually by the agency of an alkaline catalyst, and the acidity of a molecule is a rough measure of its efiicacy as a donor; while the acceptor molecule in which Z is an activating group, contains an activated double bond which is capable of polarizing and giving rise to a carbonium ion center:

@C C Z Q The efficacy as an acceptor depends upon the polarization and upon the steric environment about [S-carbon atom, as well as by the necessity that the product carbanion produced by addition of the donor be stabilized by (Arndt et al., Ann., 551,95, 1936).

The first step in the electrolytic reductive coupling reaction appears to be the addition of two electrons to form a dicarbanion from a suitably activated olefin:

The unshared electrons on the alpha-carbon atom are delocalized by'interaction with the multiple bonds of Z, while: those on the beta-carbon atom are available for nueleophilic attack upon. an appropriate substrate:

o I 1 sv o I e I Acceptor Donor Whereas the acidity of a molecule is a rather imprecise method of expressing the ability of a compound to serve as a donor in the Michael condensation, the half-wave reduction potential of a compound is a precise measure of ability to function as a donor in electrolytic reductive coupling. While the suitability of a compound as a donor molecule will depend upon the contemplated acceptor molecule and to a certain extent upon the electrolyte, in general the compound should not have a half-wave potential more negative than ca. -2.1 volts (measured against a saturated calomel electrode). As in the Michael condensation. the adduct then reacts with H+ (from the aqueous medium) or its equivalent to terminate the process. The coupling and termination reactions appear completely analogous to the corresponding steps in the Michael condensation. In both reactions the donor molecule is in competition with other, usually smaller, anions present in the reaction medium (e.g. OH- in aqueous electrolyses, OR in Michael condensations).

Since an acceptor must be able to accept electrons that are associated with a particular site in a carbanion, the half-wave reduction potential of an acceptor is not a complete criterion of its performance in this role. For example, steric factors which affect only slightly the ability to take up electrons will have a much greater effect on ability to take up a carbanion. However, if the electrolytic reduction of an activated olefin is very difiicult (i.e., it has, a very negative half-wave potential), the chances that this olefin will act as an acceptor toward an electrolytically generated carbanion are poor. In general those compounds suitable as acceptors in the Michael condensation, such as permanently polarized olefins, are also suitable as acceptors in electrolytic reductive couplings.

With some compounds, other factors must be considered. For example, compounds containing groups other than olefinic groups should not be used in reductive couplings if, at the required cathode voltages, the groups other than olefinic groups are attacked electrochemically. However, it is possible to use olefins in which an activatinclude hydrodimerizations in which one compound acts as both donor and. acceptor, as well as mixed reductive couplings in which different species of donor and acceptor are coupled. tion for the donor anion is more severe than in simple hydrodimerization, since polarized molecules of the donor-to-be molecule are of necessity available to form hydrodimer and thereby reduce the yield of mixed product. To increase the yield of mixed product, theconcentration of donor-to-be may be kept low and of acceptorto-be high. Also good results can be expected in coupling of a good acceptor, e.g., acrylonitrile, with a donor molecule which more readily accepts electrons but which because of steric effects cannot headily undergo hydrodimerization. In electrolytic reductions of highly conjugated olefins, particularly 1,3-butadiertes, it has been found that there is a considerable tendency toward simple reduction of an olefinic bond rather than hydrodirnerization. However, the reaction can often be directed toward production of the hydrodimerby using only small amounts of water in thecatholyte.

It is not necessary to describe in detail the general electrolysis conditions employed in the present invention, as

these conditions are set forth in detail in the referred-to copending applications and can be readily determined by.

those skilled in the art with the aid of the disclosure. However, in general, the electrolytic, reductive coupling will be conducted in concentrated solution in an aqueous electrolyte. It is desirable to employ fairly concentrated solutions in order to minimize undesired reactions ofintermediate ions with the water of the electrolyte. The

olefinic reactions will comprise at least 10% by ,weight of the electrolyte and preferably at least 20% by weight or more. In order to achieve such concentration, it is generally desirable to employ fairly high concentrations of salts in the electrolyte, for example, at least 10% or more by weight and preferably 20% or more by weight of the total amount of salt and water in the electrolyte. However, it is not desirable to employ such amounts of salts in the electrolyte as to make the olefinie compounds miscible with the electrolyte solution, but the use of such amounts as from 30% to 50% or so by weight of the salt ordinarily does not cause miscibility and often amounts up to or by weight of the salt in the total amount of salt'and water in the electrolyte can be employed. In some cases, the amount of water in the electrolyte is very significant to the course of the electrolysis reaction and the products produced thereby, and this should be taken into consideration in selecting suitable concentrations of the salt in the electrolyte. It will be recognized that suitable proportions of the electrolyte components in the olefinic compound can be readily determined in the light of the teaching in the present disclosure. For example, it is only necessary to see that the electrolyte has sufficient salt in it to dissolve more than 10% by weight of olefinic compound in the electrolyte, but that the electrolyte is not such a good solvent as to be miscible with the olefinic compound, and to add sufficient olefinic compounds to form a supernatant layer above the electrolyte in addition to the greater than 10% concentration dissolved in the electrolyte. As the temperature in the electrolysis cell generally rises during the electrolysis, it is desirable that the amount of olefinic compound be sufiicient to provide a supernatant layer of olefinic compound at the electrolysis temperature, as Well as at the room temperature or other temperature at which the electrolysis is started. Aside from the effect of the salt concentration on the solubility of the olefinic compounds, there is an advantage in keeping the amount of the salt In the mixed reductive coupling, competi- .tive coupling according to the present invention.

, overflow. The electrolysis procedure will, of course, produce the desired product even though some of the salt is-removed in the overflow, but the isolation of the product' is simplified if the removal of the salt is kept at a minimum. The aqueous washing medium provided in the overflow line between the cell and the boiler is useful in removing fairly large amounts of salt from the overflow liquid.

Electrolysis, of course, has been practiced for many years and numerous materials suitable as electrolytes are known, making it within the skill of the art in the light of. the present disclosure to select electrolytes for reduc- In general, any electrolyte suitable for reductive coupling can be employed in the present invention. As discussed in my copending applications, some olefinic compounds are subject to polymerization or other side reactions if the electrolyte is acidic, or excessively alkaline, and it will be advisable in such cases to conduct the reductive coupling in non-acidic solution, and in some cases below a pH at which undesirable side reactions occur, for example, below about 9.5.

In effecting the'reductive couplings according to the present invention'it is preferred to utilize a cathode hav- 1 ing an over-voltage greater than that of copper. In etfecting reductive couplings it is essential to obtain cathode potentials required for such couplings and therefore the salt employed in the electrolyte should not contain cations which are discharged at substantially lower, i.e., less negative, cathode potentials. The salt employed will ordinarily have a relatively high degree of water solubility to'permit use of concentrated solutions in order to dis- 4 solve large amounts of the organic olefinic compound.

Various other factors as discussed in my aforesaid cpendingapplications can be considered in selecting salts suitable for good results.v

In general, amine and quaternary ammonium salts are particularly suitable for use in the present process.

Among the salts which can be employed the amine and quaternary ammonium salts are generally suitable,

, especially those of sulfonic and alkyl sulfuric acids. Such salts can be the saturated aliphatic amine salts or heterocyclic amine'salts, e.g., the mono-, dior trialkylamine. salts, or the mono-, dior trialkanolamine salts, or the piperidine, pyrrolidine or morpholine salts, e.g., the ethylamine, dimethylamine' or triisopropylamine salts of various acids, especially various sulfonic acids. Especially preferred are aliphatic and heterocyclic quaternary ammonium salts, i.e., the tetraalkylammonium or the tetraalkanolammoniumsalts or'mixed alkyl alkanol ammonium'gsalts such as the alkyltrialkanolammonium, the dialkyldialkanolammonium, the alkanotrialkylammonium or the N-heterocyclic N-alkyl ammonium salts of sulfonic or other suitable acids; The saturated aliphatic or heterocyclic quaternary ammonium cations in general have suitably high cathode discharge potentials for use in the present' invention and readily form salts having suitably high water solubility with anions suitablefor use in the electrolytes employed in the'present invention. The saturated; aliphatic or heterocyclic quaternary ammonium salts are therefore-in general well adapted to dissolving high amounts of olefiniccompounds in their aqueous solutions and to effecting reductive couplings of such olefinic compounds. It is understood, of course, that it is undesirable thatthe ammonium groups contain any reactive groups which might interfere to some extent with the reductive coupling reaction. In this connection it should be noted that aromatic unsaturation as such does not interfere as benzyl substituted ammonium cations can be employed (as also can aryl sulfonate anions).

Among the anions useful in the electrolytes, the aryl and alkaryl sulfonic acids are especially suitable, for example, salts of the followingacids: benzenesufonic acid, 0-, m-, or p-toluenesulfonic acid, o-, m-, or p-ethylbenzenesulfonic acid, o-, m-, or p-cumenesulfonic acid, o-, m-, or p-tert-amyl-benzene sulfonic acid, o-, mor p-hexylbenzenesulfonic acid, o-xylcne4-sulfonic acid, p-xylene- 2-sulfonic acid, m-xylene-4- or Ssulfonic acid, mesitylene- 2-sulfonic acid, durene-3-sulfonic acid, pentamethylbenzenesulfonic acid, o-dipropylbenzene-4-sulfonic acid, alphaor beta-naphthalenesulfonic acid, o-, mor p-biphenylsulfonic acid, and alpha-methyl-beta-naphthalenesulfonic acid. Alkali metal salts are useful with certain limitations, and the alkali metal salts of such sulfonic acids can be employed, i.e., the sodium, potassium, lithium, cesium or rubidium salts such as sodiumbenzencsulfonate, potassium p-toluene-sulfonate, lithium o-biphenylsulfonate, rubidium beta-naphthalenesulfonate, cesium p-ethylbenzenesulfonate, sodium o-xylene-3-sulfonate, or potassium pentamcthylbenzenesulfonate. The salts of such sulfonic acids may also be the saturated, aliphatic amine or heterocyclic amine salts. e.g., the mono-, dior trialkyl-amine salts, or the mono-, di-, or trialkanolamine salts, or the piperidine, pyrrolidine, or morpholine salts, e.g., the

' .ethylamine, dimethylamine or triisopropylamine salt of benzenesulfonic acid or of o-, por m-toluenesulfonic acid; the isopropanolaminc, dibutanolamine or triethanolamine salt of o-, por m-toluenesulfonic acid or of o-, por m-biphenylsulfonic acid; the piperidine salt of alphaor.beta-naphthalenesulfonic acid or of the cumenesulfonic acids; the pyrrolidine salt of o-, m-, p-amyl-benzenesulfonate; the morpholine salt of benzenesulfonic acid, of o-, mor p-toluenesulfonic acid, or of alphaor beta-naphthalenesulfonic acid, etc. In general, the sulfonates of any of the ammonium cations disclosed generically or specifically herein can be employed in the present invention. The aliphatic sulfonates are prepared by reaction of the correspondingly substituted ammonium hydroxide with the sulfonic acid or with an acyl halide thereof. For example, by reaction of a sulfonic acid such as p-toluenesulfonic acid with a tetraalkylammonium hydroxide such as tetraethylammonium hydroxide there is obtained tetraethylammonium p-toluenesulfonate, use of which in the presently provided process has been found to give very good results. Other presently useful quaternary ammonium sulfonatcs are e.g., tetraethylammonium oor m-toluenesulfonate or benzenesulfo'nate; tetraethylammonium o-, mor p-cumenesulfonate or o-, mor p-ethylbenzenesulfonate, tetramethylammonium benzenesulfonate, or o-, mor p-toluenesulfonate; N,N-di-methylpiperidinium o-, mor p-toluenesulfonate or o-, mor pbiphenylsulfonate; tetrabutylammonium alphaor betanaphthalenesulfonate or 'o-, mor p-toluenesulfonate; tetrapropylammonium o-, mor p-amylbenzenesulfonate or alphaethyl-beta naphthalenesulfonate; tetraethanolammonium o-, mor p-cumenesulfona'te or o-, mor ptoluenesulfonate; tetra-butanolammonium benzenesulfonate or p-xylene-B-sulfonate; tetrapentylammonium o-, mor p-toluenesulfonate or o-, mor p-hexylbenzenesulfonate, tetrapentanolammonium p-cymene-3-sulfonate or benzencsulfonate; methyltriethylammonium o-, mor ptoluenesulfonate or mesitylene-Z-sulfonate; trimethylethylammonium o-xylene-4-sulfonate or o-, mor p-toluene sulfonate; triethylpentylammonium alphaor beta-naphthalencsulfonate or o-, mor p-butylbenzenesulfonate, trirnethylethanolammonium benzenesulfonate or o-, mor ptoluenesulfonatc; N,N-diethylpiperidinium or N-methylpyrrolidinium o-, mor p-hexylbenzenesulfonate or o-, m or p-toluenesulfonate, N,N-di-isopropyl or N,N-dibutylmorpholmium, o-, mor p-toluencsulfonate or o-, mor p-biphenylsulfonatc, etc.

The tetraalkylammonium salts of the aryl or alkarylsulfonic acids are generally preferred for use as the salt constltuents of the electrolysis solution because the electrolyses in the tetraalkylammonium sulfonates are exclusively electrochemical processes.

Among the ammonium and amine sulfonatcs useful as electrolytes in the present invention are the alkyl, aralkyl,

and heterocyclic amine and ammonium sulfonates, in which ordinarily the individual substituents on the nitrogen atom contain no more than atoms, and usually the amine or ammonium radical contains from 3 to carbon atoms. It will be understood, of course, that diand polyamines and diand poly-ammonium radicals are operable and included'by the terms amine and ammonium. The sulfonate radical can be from aryl, alkyl, alkaryl or aralkyl sulfonic acids of various molecular weights up to for example 20 carbon atoms, preferably about 6 to 20 carbon atoms, and can include one, two or more sulfonate groups. Any of the quaternary ammonium sulfonates disclosed and claimed in my copending application Ser. No. 75,130, filed December 12, 1960, can suitably be employed.

Another especially suitable class of salts for use in the present invention are the alkylsulfate salts such as methosulfate salts, particularly the amine and quaternary ammonium methosulfate salts. Methosulfate salts such as the methyltriethylammonium, trin-propylmethylammonium, triamylmethylammonium, tri-n-butylmethylammonium, etc., are very hygroscopic, and the tri-n-butylmethyL ammonium in particular forms very concentrated aqueous solutions'which dissolve large amounts of organic materials. In general the amine and ammonium cations suitable for use in'the alkylsulfate salts are the same as those for the sulfonates.

It will be recognized that the materials from which the electrolytic cell is constructed can vary considerably. In general any materials commonly employed in the construction of electrolytic cells can suitably be used. For example, the electrolytic cell can comprise a container of material capable of resisting the action of the electrolytes, for example glass. Within the container, and serving to divide it into an anode compartment and a cathode compartment may be a diaphragm in the form of a porous cup, e.g., of unglazed porcelain. The anode, which may be of, e.g., platinum or carbon, or any electrode which is inert under the reaction conditions is immersed in an anolyte contained in the porous cup. The anolyte can be aqueous solution of the salt or can be an aqueous solution of acid. When no diaphragm is employed in the cell,

stirring may be employed for pH control. Thereby the anode is subjected to little or no attack; so that the anode may be of substantially any electrode material, e.g., carbon, gold, nickel, nickel silicide, Duriron, lead and lead antimony and lead-copper alloys. An anode comprising lead deposited on a copper screen may thus be employed. The cathode, which may be mercury or another metal having a hydrogen over-voltage which is greater than that of copper, e.g., gallium, silver, gold, titanium, zirconium. thorium, cadmium, tin or lead or alloys thereof such as lead-mercury alloy or cadmium-copper alloy, and the porous cup, if one is employed, are submerged in the solution of alpha-beta-olefinic compound in the concentrated aqueous salt or a mixture of the same with a polar solvent. The entire cell may be cooled by a jacket containing a coolant, and both the anode and cathode chambers may be equipped with condensers. However as will be hereinafter shown, the increase of temperature which is produced during electrolysis generally does not result in so much of a decrease in yield that cooling other than with circulating water is economically required. Generally, the electrolysis can be conducted at a temperature of from, say, 10 C. and up to almost the refluxing temperature of the electrolytic bath. Stirring of the solution during the electrolyses, if desired-may be conducted by mechanical .or magnetic means. During the electrolysis, the pH of the catholyte may be controlled by addition of small amounts of acid as necessary to prevent the catholyte from becoming more alkaline than desired. The quantity of current which is supplied to the cell will vary with the nature and quantity of the bath and of the electrodes and with the operating temperature, but will ordinarily be at a rate greater than 0.5 ampere and in the order of a current density, of, say, from 2.0 to 20.0

amperes/dm? (dm. refers to the area in square decimeters of electrode surface). The efiiciency of the process is, to some extent, dependent on the current density used. Thus for the efiicient production of adiponitrile, using a mercury cathode, it has been found that the current density should be from about 5 to 15 amperes/din The etficiency falls as the current density is decreased.

Example 1 An electrolysis of acrylonitrile was conducted on a continuous basis in an apparatus of the type illustrated in the figure to produce adiponitrile. The electrolysis cell utilized 185 milliliters of mercury as the cathode and for the anode a platinum wire was hooked to a platinum screen. For the catholyte, about 250 grams of approximately a forty percent solution of tetracthylammonium paratoluene-sulfonate was employed and grams of acrylonitrile was added thereto. As the anolyte, an approximately thirty-five percent solution of the same salt was employed in an amount of 70 milliliters. Approximately 136 milliliters of additional acrylonitrile was added to the catholyte to reach the overflow point, and 330 milliliters acrylonitrile was placed in the boiler. The height of water in the boiler was approximately 4 inches above the disperser. The elecrolysis was conducted at 3.5 to 5 amperes for a total of about 19.5 ampere hours, and at a cell voltage of 24 to 28 volts. The cell temperature varied from 30 to 40 C. During the procedure several samples were withdrawn from the aqueous layer of the washer. being replaced by fresh water, while the withdrawn material was concentrated and returned to the electrolysis cell. Following the electrolysis. the boiler contents were diluted with 220 milliliters methylene dichloride, washed three times with'75 milliliters water, and dried over calcium sulfate. The methylene chloride was removed by distillation to leave 170 grams of higher boiling material.

.The material was analyzed by vapor-phase chromatography to show that it contained 19.2 grams of adiponitrile. The organic layer in the electrolysis cell was similarly treated to give about 340 grams of organic material, of which 7.5 grams was adiponitrile. The aqueous layer in the electrolysis cell was diluted with 300 milliliters of water, washed three times with portions of methylene dichloride, and dried over calcium sulfate and concentrated to about 31 grame by distilling off the methylene dichloride. This residue contained less than a gram of adiponitrile. It is thus demonstrated that the described procedure is effective for extracting the adiponitrile product from the catholyte and that the adiponitrile product can then readily be recovered from the materials in the boiler. Various refinements or changes can be employed in the extraction or washing procedures and the recycling of olefinlc compounds or electrolyte materials to the electrolysis cell, as will be readily apparent to those skilled in the art in view of the present disclosure.

Example 2 Acrylonitrile was continuously hydrodimerized in apparatus of the type described in Example I. As a cathode, milliliters mercury was employed, and the catholyte was composed of approximately 250 grams of aqueous tetraethylammonium p-toluenesulfonate solution of a concentration such thatit did not quite dissolve the 75 grams of acrylonitrile employed, as an upper layer of about 1.5 inches acrylonitrile was present. About 200 milliliters acrylonitrile was placed in the boiler. The anode employed was a platinum screen to which the platinum lead wire was attached by a glass-sealed contact. As anolyte, 70 milliliters aqueous tetraethylammonium ptoluenesulfonate was employed. The cooling-water was circulated through the condenser and distillation of the acrylonitrile from the boiler was commenced to start the circulation of the solvent for the extraction phase of the procedure. With the catholyte faintly alkaline, electrolysis was conducted at 3 to 4 amperes for 6 hours.

Cit

acrylonitrile layer to one inch. The materialin the boiler,

the acrylonitrile layer and the aqueous catholyte were removed and separated without distillation. The acrylonitrile layer was washed with an alkaline aqueous solution, dried over calcium sulfate and then part of the acrylonitrile was stripped therefrom by'distillation. The residue of 96 grams was analyzed by vapor phase chromatography which showed it was 1.7% adiponitrile. The 'boiler material was diluted with water, extracted with methylene dichloride and dried over calcium sulfate. The methylene dichloride was removed by distillation to leave 114 grams of material which vapor phase chromatography showed to be 25% .adiponitrile. Attempted isolation of adiponitrile from the aqueous catholyte indicated that no adiponitrile had remained in that layer of the system.

It will be appreciated that the use of acrylonitrile in the above examples is exemplary and that other olefinic compounds can be reductively coupled or hydrodimcrized in similar procedures. For example, in hydrodimerization of crotonitrile'or ethyl acrylate, solutions of salts,,such as tetraethylammon ium p-toluenesulfonate or tetraethylammoniummethylsulfate, should be used in such concentration as required to dissolve 20 to 30% of the olefin, which will generally require that 20 to 50% or so of the salt and water content be salt, or with some salts that'as much as 70% be salt or that auxiliary solvents be provided.

In the case where it is planned to reductively couple two ditferentolefinie compounds, either or both of the olefinic compounds can be provided in excess of solubility in the'electrolyte and utilized asthe extracting solvent.-

To increase the yield of mixed product, however, it is generally advisable to keep the concentration of donor-tobe low and that of the aeceptor-to-be highwhich can be done by using the acceptor-to-be as the extracting solvent and only having small amounts of the donor-to-be present and replenishing it as it reacts. In cases where one olefin has very limited solubility in the catholyte while the other olefin has greater solubility, it may be desirable to use the olefin of very limited-solubility asextracting solvent,

and this-limited solubility also provides another way in some cases of insuring only a low concentration of the donor-to-be molecule. It will be recognized that the extracting solvent mustbe capable of dissolving and extracting the coupled product from the electrolyte, but in general the coupled product will have a fair degree of solubility in the olefinic monomers. It will also be recognized that in the particular gravity-overflow system illustrated in the figure of the drawing, it will be necessary that theextracting solvent have a lower specific gravity than the catholyte, but the olefinic compounds employed are generally characterized by lower specific gravity than aqueous electrolytes. other organic solvents in conjunction with the olefinic compounds as extracting solvent, provided that such organic solvent should not extract the olefinic compound from the catholyte to such a degree that reductive coupling cannot be ellfected at' a suitable rate.

The application of the present invention to processes in which two different compounds are coupled often makes it advantageous to employ special techniques. For example, if a donor-to-be molecule used in small amounts is readily soluble in the acceptor-to-be molecule used as extractant, there is the possibility that it could be completely extracted from the electrolyte. If it should boil lower than the acceptor-to-be, however, this possibility would be avoided by recycling the distillate in the usual way; if it should boil higher, it would be advisable to have In some cases it may be desirable to use 'ponitrile or approximately 10 grams adiponitrile.

a second distillation zone to remove the donor-to-be from the product subsequent to removing the acceptorto-be in a first distillation zone, and to recycle both distillatcs; or, in this latter case it might be preferable to simply add donor-to-be, continuously or intermittently, to the electrolyte during the electrolysis and to separate the donor-to-be from the product for re-use only as convenient in the normal procedures for isolating and purifying the product.

Many variations other than those illustrated herein can be employed and are considered within the scope of the invention. I

Example 3 For this procedure, a cell similar to that illustrated in the figure is suitable, except that the equipment providing for overflow, extraction, distillation and return of distillate is not necessary; i.e., the overflow tube, washer, boiler, condenser and disperser can be dispensed with and the electrolysis can be conducted in a vessel having an opening only at the top, although an opening at the bottom provided with a stopcock. or valve may be convenient to permit emptying the contents after the electrolysis. Acrylonitrile was hydrodimerized in a procedure em ploying as catholyte 195 grams of 34.7 weight percent tetraethylammonium p-toluenesulfonate containing 44 grams acrylonitrile.

As a cathode, 110 milliliters mercury was employed. A current of'3 amperes was used for the electrolysis for about three hours, with the cathode voltage (vs. saturated calomel electrode) being -1.82. The catholyte (containing acrylonitrile as well as product) was transferred to another container and extracted with a 100 milliliter portion of acrylonitrile. The resulting acrylonitrile solution was then washed twice with 10 milliliter portions of water, and 4.5 grams salt was obtained. The acrylonitrile solution was then dried over calcium sulfate and part of the acrylonitrile was removed by distillation to leave 42 grams of material, which analyzed by vapor phase chromatography as 23.6% adi- The aqueous catholyte was then extracted a number of times with methylene dichloride, and after the bulk ofthe methylene dichloride was distilled oil, 43 grams of material remained, but vapor phase chromatography indicated only about 5% or about 2.2 grams was adiponitrile. Thus it is demonstrated that a simple washing procedure with acrylonitrile removes practically all of the product from the electrolyte, and removes very little of the electrolytic salt. Additional extractions with acrylonitrile could be employed to remove substantially all of the adiponitrile from the electrolyte.

What is claimed is:

1. In the electrolytic reductive coupling of olefinic compounds selected from the group consisting of alpha, beta-olefinic nitriles,,esters and carboxamides and mixtures of the same by electrolysis in an aqueous salt elec trolyte solution in contact with the cathode of an electrolysis cell and recovery of the reduced coupled product, the concentration of salt in aqueous solution being such that the solution is capable of dissolving at least 10% by weight of olefinic compound but is not completely miscible with the olefinic compound, the improvement which comprises contacting the aforesaid aqueous salt electrolyte solution with liquid olefinic compound in excess of its solubility in ithe aqueous salt electrolyte solution thereby extracting reduced coupled product into the thus obtained liquid olefinic compound phase, the olefinic compound being one which is being reductively coupled in the process, and separating the liquid olefinic compound phase containing reduced coupled product dissolved therein from the aqueous salt electrolytesolution, and separating the reduced coupled product'from the liquid olefin compound phase.

2. The prpcess of claim 1 in which the reductive coul3 filing is a hydrodimcrization and the compound being hydrodimcrizcd is used for the extraction.

3. The process of claim 2 in which the compound being hydrodimerized is acrylonitrile and in which the extraction procedure is conducted separately from the electrolysis.

4. In the electrolytic reductive coupling of olefinic compounds selected from the group consisting of alpha, beta-olefinic nitriles, esters and carboxamides and mixtures of the same in anaqueous salt electrolyte solution in .contact with the cathode of an electrolysis cell and recovery of the reduced coupled product, the improvement which comprises employing liquid olefinic compound which is being reductively coupled in an amount greater than its solubility in the aqeous salt electrolyte solution so as to form a liquid. supernatant layer above the aqueous salt electrolyte solution during the electrolysis and removing liquid supernatant layer along with reduced coupled product dissolved therein.

5. The process of claim 4 in which the olefinic compound is separated from the product and returned to the electrolyte. I v

6. The process of claim 4 in which the supernatant layer is permitted to overflow from the electrolysis cell and the olefinic compound is then distilled from the overflow and returned to the electrolyte.

7. The method of producing a reduced coupled product of olefinic compounds which comprises subjecting an aqueous salt electrolyte solution of olefinic compound from the group consisting falpha,beta olefinic nitriles, esters and carboxamides and mixtures of the same to electrolysis by passing electric current through the solution in contact with a cathode having a hydrogen over-voltage greater than that of copper, causing development of the cathode potential required for hydrodimerization of at least one selected olefinic compound, the solution having a non-acidic pH and comprising at least by weight of olefinic compound dissolved therein and sufficient of a liquid olefinic compound which is being reductively coupled to provide a liquid supernatant layer of olefinic compound above the surface thereof during electrolysis, and removing the liquid supernatant layer along with reduced, coupled product dissolved therein.

8. The method of claim 7 in which additional olefinic compound is added during the electrolysis below the surface of the solution to aid in extracting reduced, coupled product therefrom.

9. The method of claim 8 in which acrylonitrile is employed as olefinic compound.

supernatant acrylonitrile along with adiponitrile product dissolved therein, separating acrylonitrile from the prod uct and returning the separated acrylonitrile to the electrolyte.

12. The method of claim 11. in which the supernatant layer is permitted to overflow from the electrolysis .cell and the acrylonitrile is distilled from the overflow and returned to the cell below the surface of the electrolyte.

13. The method of claim 12 in which the overflow is conducted through an aqueous wash prior to distillation. 14. In the production and recovery of adiponitrile by electrolytic hydrodimerization of acrylonitrile by electrolysis in aqueous salt electrolyte solution in contact with the cathode of an electrolysis cell and recovery of adiponitrile therefrom, the improvement which comprises contacting the aqueous salt electrolyte solution with acrylonitrile in excess of its solubility in the aqueous salt electrolyte solution so that adiponitrile is extracted from the aqueous salt electrolyte solution into the thus obtained liquid acrylonitrile phase, and separating the liquid acrylonitrile phase containing dissolved adiponitrile from the aqueous salt electrolyte solution, and separating the adiponitrile from the acrylonitrile phase.

15. In the production and recovery of adiponitrile by electrolytic hydrodimerization of acrylonitrile by electrolysis in aqueous salt electrolyte solution in contact with the cathode of an electrolysis cell and recovery of adiponitrile therefrom, the improvement which comprises washing the aqueous salt electrolyte solution with amounts of acrylonitrile in excess of its solubility in the aqueous .saltelectrolyte solution thereby extracting the adiponifrom, and separating the adiponitrile from the said acrylo- 'nitrile wash liquor.

'16. The method of claim 14 in which the aqueous salt electrolyte solution is non-acidic and has a pH below about 9.5 and the concentration of the acrylonitrile in the aqueous salt electrolyte solution is greater than 10% by weight, and the cathode has a hydrogen over-voltage greater than that of copper.

References Cited by the Examiner UNITED STATES PATENTS 2,632,729 3/53 Woodman 204-72 2,700,021 1/55 Elofson 20473 2,726,204 12/ Park et al 20472 2,749,293 6/56 Wahlin 204--73 2,944,957 7/60 Keidel 204275 2,972,573 2/ 61 Capaccini 204-275 FOREIGN PATENTS 566,274 11/58 Canada.

- JOHN H. MACK, Primary Examiner.

JOSEPH REBOLD,MURRAY TILLMAN, WINSTON A. DOUGLAS, Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,193,477 July 6, 1965 Manuel M. Baizer It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 68, for "YCH Y" read XCH Y column 5,

line 8, after "about" insert the line 19, for "551" read H 521 column 6, line 20, for "headily" read readily column 10, line 25, for "elecrolysis" read electrolysis line 44, for "grame" read grams column 13, line 15, for "aqeous" read aqueous line 59, for "in the electrolyte aqueous salt solution" read in the aqueous salt electrolyte solution Signed and sealed this 6th day of June 1967.

(SEAL) Attest:

EDWARD M. FLETCHER, JR- EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN THE ELECTROLYTIC REDUCTIVE COUPLING OF OLEFINIC COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF ALPHA, BETA-OLEFINIC NITRILES, ESTERS AND CARBOXAMIDES AND MIXTURES OF THE SAME BY ELECTROLYSIS IN AN QUEOUS SALT ELECTROLYTE SOLUTION IN CONTACT WITH THE CATHODE OF AN ELECTROLYSIS CELL AND RECOVERY OF THE REDUCED COUPLED PRODUCT, THE CONCENTRATION OF SALT IN AQUEOUS SOLUTION BEING SUCH THAT THE SOLUTION IS CAPABLE OF DISSOLVING AT LEAST 10% BY WEIGHT OF OLEFINIC COMPOUND BUT IS NOT COMPLETELY MISCIBLE WITH THE OLEFINIC COMPOUND, THE IMPROVEMENT WHICH COMPRISES CONTACTING THE AFORESAID AQUEOUS SALT ELECTROLYTE SOLUTION WITH LIQUID OLEFINIC COMPOUND IN EXCESS OF ITS SOLUBILITY IN THE AQUEOUS SALT ELECTROLYTE SOLUTION THEREBY EXTRACTING REDUCED COUPLED PRODUCT INTO THE THUS OBTAINED 